WO2005098062A1

WO2005098062A1 - Waste-free hydrometallurgical extraction of magnesium and other metals from rock formations of varying olivine content

Info

Publication number: WO2005098062A1
Application number: PCT/AM2005/000001
Authority: WO
Inventors: Hovhannes Hovhannisyan; Stepan Abovyan; Gagik Karamyan
Original assignee: Hovhannes Hovhannisyan; Stepan Abovyan; Gagik Karamyan
Priority date: 2004-04-05
Filing date: 2005-03-22
Publication date: 2005-10-20

Abstract

The invention relates to the methods of extraction of metals, their chlorides, oxides and hydroxides from ultrabasic and basic rocks. This wasteless method include the steps of rock crushing and grinding, subsequent lixiviation in hydrochloric acid with obtaining a dissolved part in the form of chlorides of magnesium and other metals, and an undissolved solid part in the form of silicon dioxide and other minerals. According to the invention the silicate part of the rockforming mineral olivine and its metamorphic varieties is calcined before dissolution. The leach mixture obtained in the process of dissolution is separated by precipitation into liquid and solid fractions. Then the dissolved fraction is transferred into oxides and hydroxides, which then are reduced to the elemental metals, while silicon dioxide is separated from undissolved part, washed and dried. The goal of invention is integrated extraction of all valuable products from mentioned rocks and their metamorphic varieties.

Description

WASTE-FREE HYDROMETALLURGICAL EXTRACTION OF MAGNESIUM AND OTHER METALS FROM ROCK FORMATIONS OF VARYING OLIVINE CONTENT

Technical Filed This invention relates to the methods of extraction of metals, their chlorides, oxides, hydroxides from the rocks and can be used for wasteless, complete and environmentally sound extraction of valuable products from ultrabasic rocks and their metamorphic varieties such as serpentinites, hardwoods, etc, as well as basic rocks which are transient from ultrabasic to basic, wherein content of olivine and its varieties is from 5 to 50 %.

Background Art It is known the process of production of metallic magnesium, pure magnesium oxide by processing of source feed stock by the method of carbothermal reduction of original material, for example, magnesium oxide containing small quantity of Fe, Si, Ca, Al and/or magnesium-silica minerals, for example, olivine, at pressure bellow atmospheric [1]. Metallic magnesium is evaporated in reduction zone, and in the second condensation zone the metallic magnesium and pure magnesium oxide are deposited. Silicon is partially evaporated in the form of SiO which is deposited in the first condensation zone which is located before second condensation zone, and than it is transformed in reaction mixture into SiC and Si-Fe alloy. The drawback of this method is high energy consumption, expensiveness caused by the using of pyrolized carbon and two-stage production method, as well as environmental vulnerability and restricted applicability. The most related method by technical essence consists in processing of metamorphic formation of ultramafic rocks and minerals, namely serpentinite and forsterite, by their crushing and grinding, and subsequent dissolution in hydrochloric acid resulting in dissolved fraction in the form of magnesium chloride, and undissolved fraction in the form of silicon dioxide [2]. By following thermal treatment and dewatering magnesium chloride is transformed into magnesium hydroxide which is saturated by carbon dioxide to form MgCO₃. The disadvantage of this method is the limited utility conditioned by extraction and enrichment of only serpentinite and forsterite rocks containing 90% of magnesium and silicon compounds. Besides, in mentioned method the most useful products obtained after dissolution of the rock remain untapped. The objective of presented invention is integrated extraction of all useful products from the ultrabasic rocks and their metamorphic varieties, such as serpentinites, hardwoods, etc., as well as basic transition (from ultrabasic to basic) rocks, such as norites, habro-norites, olivinic habro, anorthosites and troctolites, wherein the amount of rockforming mineral, olivine (Mg,Fe)₂SiO₄ , and its metamorphic varieties is in the range 5 - 50 %. Disclosure of the Invention

The essence of the invention consists in wasteless method of metals and their compounds extraction from ultrabasic and transition (from ultrabasic to basic) rocks, comprising the stages of crushing and grinding of said rocks with following dissolution in hydrochloric acid and obtaining the dissolved part in the form of chlorides of magnesium and other metals, and undissolved part in the form silicon dioxide and other minerals, according to the invention, the silicate part of the rockforming mineral olivine and its metamorphic varieties are subjected to dissolution, said minerals before dissolution they are calcined, the mixture obtained in the result of dissolution is separated by precipitation on dissolved and solid undissolved parts, magnesium chloride and other salts are separated and transferred into corresponding oxides and hydroxides, which then are reduced to the metallic form, while undissolved part of the rock is separated, from which SiO₂ is extracted, washed, dewatered and dried. The original rock is grinded up to grain size less than 1 mm that is calcined at temperatures bellow 1000 °C during time interval 5 - 120 min. Magnesium chloride and other salts are separated and purified by the methods of electro-membrane separation or chemical precipitation. The separation of undissolved part is performed by chemical, gravitational or electromagnetic methods. With the aim of production of pure and extrapure metals the obtained hydroxides and oxides are subjected to selective reduction by the methods of hydrogen, cathodic or high temperature metallurgical vacuum electron-beam reduction and casting depending on nature of metal and necessary purity. For obtaining of product material with 99 % purity, silicon dioxide is washed, dewatered and dried, while for obtaining polycrystalline and monocrystalline silicon SiO₂ is subjected to additional purification and transferred to the electron-beam furnace. Other undissolved mineral species and native metals amounting 0.1 - 1.0 % of the rock are subjected to selective enrichment by gravitational, electromagnetic and chemical methods, whereupon, for pure and extrapure metal production, these materials are subjected to selective reduction by the methods of hydrogen, cathodic, or high temperature metallurgical vacuum electron-beam processing and casting depending on metal nature and its necessary purity, thereby. The technological chart of the rock processing according to the invention is following:

ED* - electro-membrane. The embodiment of the invention can be illustrated as following. Basic and ultrabasic rocks manifested by massifs containing from 50 to 95 % of rockforming mineral olivine, with depth occurrence of 2000 m and more, are recovered from the deposit by known methods, like excavation, whereupon they are crushed, grinded up to particle size less than 1 mm, calcined if necessary, for water removal and activation at temperature up to 1000 °C during time interval from 5 to 120 min. Then silicate part of the of rockforming mineral olivine and its metamorphic varieties is dissolved in diluted hydrochloric acid having concentration of 10 - 30 % of concentrated acid, predominantly 20%. Dissolution of the rockforming mineral olivine (Mg,Fe)₂SiO₄ by hydrochloric acid may be presented by following general formula:

(Mg,Fe)₂SiO₄ + 4HC1 = 2MgCl₂ + 2FeCl₂ + SiO₂ + 2H₂O +Q

Dissolution performed in special designed acid resistant reactors with agitation accompanied with evolution of big amount of thermal energy which can be used also for heating of rooms and power production. The process of dissolution is carried out in closed cycle during time interval from 5 to 300 min depending on extent of rock powdering, its activity and acid concentration. Then hydrochloric acid is regenerated and recycled by special pipeline back to the dissolution stage. After immersing of powdered rock into hydrochloric acid in special reactors with acid resistant coating and rotary agitation all soluble metals in the form of isomoφhic impurities and accessory minerals are leached and pass into solution, while undissolved part together with silicon dioxide is precipitated. Silicon dioxide and undissolved metals and minerals are separated by modern separation technique such as gravitational, chemical, electromagnetic, while SiO₂ intended for production as 99 % purity powder is washed, dewatered, dried and stored. In the case of necessity, for polycrystalline or monocrystalline silicon production, SiO₂ is subjected to additional chemical purification and directed into the vacuum electron-beam furnace. Other undissolved mineral species and native metals amounting 0.1 - 1.0 % of the rock are subjected to selective enrichment by the gravitational, electromagnetic and chemical methods, then with the aim of production of pure and extrapure metals, these materials are subjected to selective reduction by the methods of hydrogen, cathodic, or high temperature metallurgical vacuum electron-beam reduction and casting. Dissolved rock species in the form of chlorides of magnesium and other metals are separated and purified by the methods of electro-membrane separation or chemical precipitation, therewith MgCl₂ is transferred to Mg(OH)₂ and then to MgO. Remaining metal chlorides similar to above mentioned process are converted into corresponding hydroxides and oxides with subsequent electrochemical regeneration and recovering of hydrochloric acid and water back to the dissolution stage. With the aim of production of pure and ultrapure metals the hydroxides and oxides including MgO are subjected to selective reduction by the methods of hydrogen, cathodic, or high temperature metallurgical vacuum electron-beam reduction and casting depending on nature of metal and necessary purity. Produced MgO after high temperature treatment can be used for production of refractory materials, dead-burned magnesia for medicine and agriculture as high quality mineral fertilizer, or in combination with MgCl₂ for Sorel cement production.

Example of the processing of ultrabasic dunite rock

Dunites represent about 15% of the all ultrabasic rocks. As a starting material dunite was used from rock pieces with the size of 200 - 500 mm. For guarantee of production cycle of recovery of metals and their compounds from dunite containing 90% of olivine mineral, it is grinded by jaw and conic breakers up to average size of 20 mm. Then humidity of the crushed rock was determined by drying of definite mass in the oven at temperature of 120 °C up to constant weight. If humidity is more than 2 %, the crushed rock before further powdering is calcined up to 600 °C during 2 hours for full dewatering and activation, then the preliminary crushed rock is grinded up to particle size of 0.9 mm in ball mill. Then 1 kg of powdered rock was filled into enameled reactor with mechanical mixer, poured with 1 1 of concentrated (1.1 g/1 density) hydrochloric acid. In the process of agitation and rock dissolution during 10 min the solution is self-heated resulting in temperature increase up to 100 °C. Undissolved part comprising 97 - 98 % of silicon oxide was extracted from the bottom of reactor, while dissolved part comprising 85 % of magnesium chloride and 10 % of iron oxide was separated for further transferring into hydroxides and oxides.

The extracted silicon dioxide and small admixtures amounting about 1 w. % and consisting mainly from chromospinelides in unbound state, were separated on the gravitational table SKO-5 with simultaneous washing and with subsequent water cleaning and turning back. The gravitational enrichment and separation is performed with very high efficiency due to more than 5 times difference between specific densities of SiO₂ (p = 2.3 g/cm²) and chromospinelides (p = 10 g/cm²). In the result the undissolved part of rock is separated onto 400 g of SiO₂ and 8 g of chromospinelides (FeCr₂O₄) which were dried in oven during 2 hours. The resulting product is 99 % silicon dioxide and pure chromospinelide in the form of powder with micronsize particles. Dissolved rock components, mainly MgCl₂ and FeCI₂, were separated by addition of ammonium hydroxide NH₄OH (about 50 g) up to solution pH of 5-6 resulting in precipitation of iron hydroxide, Fe(OH)₂, which is extracted by separation on the centrifuge. Than the solution is returned back for further extraction of magnesium hydroxide, Mg(OH)₂ by increasing of pH value up to 1 1-12 which is performed by addition of ammonium hydroxide in amount of 100 g. For obtaining pure and extrapure (99.99%) hydroxides the obtained magnesium hydroxide is subjected to treatment in electrodialysis apparatus with applied voltage of 8 - 10 V. In the result pure and extrapure magnesium hydroxide is obtained. By means of the same electro-membrane method and constant voltage the pure and extrapure iron hydroxides Fe(OH)₂ are produced by cleaning them from impurities. The content of magnesium and iron hydroxides is 75 and 20% of all dissolved part. The ions of other metallic admixtures which amount is less than 1 % can be extracted by the same method. For production of pure valuable metals and oxides, the magnesium and iron hydroxides are subjected to heat treatment at temperatures over 600 °C, whereupon 420 g of MgO and 95 g of Fe O₃ are obtained in the form of pure fine powder with particle size of 10 microns. For production of pure and extrapure metals the extracted oxides in the form of powder are filled into the molds positioned into the vacuum furnace. After evacuation up to pressure of 10^"4 torr the furnace was heated up to melting temperatures, 1 100 °C for iron and 1900 °C for magnesium. After cooling up 65 g of reduced iron and 250 g of magnesium were removed from the molds in the form of ingots with purity of 99.99%.

Example of processing of basic transition troctolite rock Among intrusive habro-peridodite formations the basic rocks contain olivine and its metamorphic varieties in quantities of 5 - 50 %, one of which is troctolite containing 25 -50% of olivine and their metamorphic varieties. Troctolites amount about 3% of all basic rocks.

As original material the troctolite was selected in the form of pieces with dimensions of 300-700 mm. For providing the production cycle of recovery of metals and their compounds from troctolite containing 40% of olivine mineral, it is crushed by jaw and conic breakers up to average size of 20 mm. Then humidity of the crushed rock was determined by drying of the definite mass in the oven at temperature of 120 °C up to constant weight. If humidity is more than 2%, the crushed rock before further powdering is calcined up to 800 °C during 2 hours for full dewatering and activation, then the preliminary crushed rock is grinded up to particle size of 0.7 mm in ball mill. Then 1 kg of powdered rock was filled into enameled reactor with mechanical mixer, poured with 1 1 of concentrated (1.1 g/1 density) hydrochloric acid. In the process of mixing and rock dissolution during 8 min the solution is self-heated resulting in temperature increase up to 100 °C. Undissolved part comprising 97 - 98 % of silicon oxide was extracted from the bottom of reactor, while dissolved part comprising 85 % of magnesium chloride and 10 % of iron oxide was separated for further transferring into hydroxides and oxides. The extracted silicon dioxide and small admixtures amounting about 2 % and consisting mainly from chromospinelides with high quantity of aluminum (about 17% of the total chemical content) were separated on the gravitational table SKO-5 with simultaneous washing and with subsequent water cleaning and turning back. The gravitational enrichment and separation is performed with very high efficiency due to more than 4 times difference between specific densities of SiO₂ (p = 2.3 g/cm²) and chromospinelides (p = 8 g/cm²). In the result, the undissolved part of rock is separated onto 360 g of SiO₂ and 20 g of chromospinelides (FeCr₂O₄) which were dried in oven at 200 °C during 2 hours. The resulting product is 99 % silicon dioxide and pure chromospinelide in the form of powder with micronsize particles. Dissolved rock components, mainly MgCl₂ and FeCI , were separated by addition of ammonium hydroxide NH OH (about 50 g) up to solution pH of 5-6 which results in precipitation of iron hydroxide, Fe(OH)₂, which were extracted by separation on the centrifuge. Than additional 40 g of ammonium hydroxide was introduced into the solution changing pH value up to 8 resulting in aluminum hydroxide precipitation. Then centrifugal extraction of these metal hydroxides is carried out, first iron and then aluminum. Solution containing MgCl₂ is returned back and subjected to further treatment for extraction of magnesium hydroxide, Mg(OH)₂ by increasing of pH value up to 1 1-12 which is performed by addition of ammonium hydroxide in amount of 100 g. For obtaining pure (99%) and extrapure (99.99%) hydroxides the obtained magnesium hydroxide is subjected to treatment in electrodialysis apparatus. By means of the same electro-membrane system pure and extrapure iron and aluminum hydroxides are produced by cleaning them from impurities. In the result 30% of Mg(OH)₂ , 45% of AI(OH)₃ and 15% of Fe(OH)₂ are obtained. The ions of other metallic admixtures which amount is less than 1.5 % of overall rock content may be extracted by the same method. For production of pure valuable metals and oxides, the magnesium, aluminum and iron hydroxides are subjected to heat treatment at temperatures over 700 °C. In the result, 150 g of MgO, 220 g Al O₃ and 70 g of Fe₂O₃ are obtained in the form of pure fine powder with particle size of 10 microns. For production of pure and extrapure metals the extracted oxides in the powder form are filled into the mold positioned into the vacuum oven. After evacuation up to pressure of 10^"4 torr the furnace was heated up to melting temperatures, 1 100 °C for iron, 1750 °C for aluminum and 1900 °C for magnesium. After cooling up the reduced metals, 90 g of magnesium, 115 g of aluminum and 50 g of iron were removed from the molds in the form of ingots with purity of 99.99%. By the same method other metals are obtained which content is less than 1.5% of total rock mass. Thus, proposed method provides integrated extraction of all valuable products from ultrabasic rocks and their metamorphic varieties such as serpentinites, hardwoods, etc, as well as from basic transient rocks including norites, habro-norites, olivinic habro, anortosites and troctolites, wherein the content of rockforming mineral olivine (MgFe) SiO₄ and its metamorphic varieties varies from 5 to 50 %. Basic rocks containing olivine and its metamorphic varieties break in the result of chemical dissolution of olivine and its metamorphic varieties, which at mentioned breakage exert dynamic pressure on the rockforming mineral plagioclase with formation of various rings and cracks resulting full collapse and dissolution. Proposed method is environmentally sound and allows complete and wasteless extraction of valuable products from the rock, and recover employed chemicals without emission into environment and hazardous health effect. Besides, proposed method allows grinding of the rock into more coarse particles (up to 1 mm) instead of 45 microns which is necessary in the case of known methods of magnesium rock processing for metals and oxides production by carbothermal reduction. This leads to the saving of electrical energy, reduction of laboriousness and ecological compatibility. The invention has been made owing to versatile geological, petrographycal, mineralogical, physical and chemical methods of rock investigations, as well as studying of heterogeneous processes simulating geomorphology of minerals in the nature, which made it possible to understand the mechanisms of the dissolution processes of various mineral including basic rocks.

References

[1] RU 2109078, Int.Cl. C22B26/22, 10.04.1998.

[2] "Carbon Dioxide Disposal in Mineral Form", Los Alamos National Laboratory, LA-UR- 97-2094, 1997.

Claims

1. Wasteless method of extraction metals and their compounds from ultrabasic rocks and transient rocks between ultrabasic and basic, comprising crushing and grinding of said rocks, dissolution in hydrochloric acid by following obtaining of dissolved fraction in the form of magnesium and other metal chlorides and undissolved fraction in the form of silicon dioxide and other minerals, characterized by dissolution of silicate part of the rockforming mineral olivine and its metamorphic varieties in hydrochloric acid, at that before dissolution these minerals are calcined, and mixture obtained in the process of dissolution is separated by precipitation on liquid and solid fractions, dissolved part comprising magnesium chloride and other salts are transferred into corresponding oxides and hydroxides, which are reduced than to the metals, while silicon dioxide is separated from undissolved part, washed, dewatered and dried.

2. Method according to claim 1 , characterized by grinding of the original rock up to particle size less than 1 mm.

3. Method according to claim 1 , characterized by calcination of grinded rock particles at temperatures up to 1000 °C during 5 - 120 minutes.

4. Method according to claim 1 , characterized by separation and purification of magnesium chloride and other dissolved salts by electro-membrane method and chemical precipitation.

5. Method according to claim 1, characterized by separation of undissolved fractions by chemical, gravitational and electromagnetic methods.

6. Method according to claim 1 , characterized by obtaining of metals from corresponding hydroxides and oxides by hydrogen, cathodic, chemical or high-temperature vacuum processes, for example electron-beam reduction and casting.